java - Android ViewPager doesn't show Fragment -

i'm trying let viewpager show fragments, however, doesn't seem work. not showing anything, not height. can tell me step missing? thanks

main_activity.xml:

<android.support.design.widget.coordinatorlayout     xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@color/colorbackground">      <android.support.v4.view.viewpager         android:id="@+id/viewpager"         android:layout_width="match_parent"         android:layout_height="match_parent"         android:layout_above="@+id/bottomnavigation" />      <com.aurelhubert.ahbottomnavigation.ahbottomnavigation         android:id="@+id/bottomnavigation"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:layout_gravity="bottom" />  </android.support.design.widget.coordinatorlayout> 

mainactivity.java:

public class mainactivity extends appcompatactivity {      private static final string tag = "mainactivity";      ahbottomnavigation bottomnavigation;     viewpager viewpager;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);          setcontentview(r.layout.activity_main);         bottomnavigation = (ahbottomnavigation) findviewbyid(r.id.bottomnavigation);         viewpager = (viewpager) findviewbyid(r.id.viewpager);         viewpageradapter pageradapter = new viewpageradapter(getsupportfragmentmanager());          // buttom navigation         // add items         ahbottomnavigationitem item1 = new ahbottomnavigationitem("rooms", r.drawable.ic_chatboxes);         ahbottomnavigationitem item2 = new ahbottomnavigationitem("user", r.drawable.ic_contact_outline);         bottomnavigation.additem(item1);         bottomnavigation.additem(item2);         // customize buttom navigation         bottomnavigation.settitlestate(ahbottomnavigation.titlestate.always_show);         // set colors         bottomnavigation.setaccentcolor(contextcompat.getcolor(this, r.color.coloraccent));         bottomnavigation.setinactivecolor(contextcompat.getcolor(this, r.color.colortabdefault));         // set background color         bottomnavigation.setdefaultbackgroundcolor(contextcompat.getcolor(this, r.color.colorbackground));         bottomnavigation.settranslucentnavigationenabled(true);          // viewpager setup         pageradapter.addfragment(new rooms(), "rooms");         pageradapter.addfragment(new user(), "user");         viewpager.setadapter(pageradapter);         viewpager.setcurrentitem(bottomnavigation.getcurrentitem());         viewpager.addonpagechangelistener(new viewpager.onpagechangelistener() {              @override             public void onpagescrolled(int position, float positionoffset, int positionoffsetpixels) {              }              @override             public void onpageselected(int position) {                 bottomnavigation.setcurrentitem(position);             }              @override             public void onpagescrollstatechanged(int state) {              }         });         bottomnavigation.setontabselectedlistener(new ahbottomnavigation.ontabselectedlistener() {             @override             public boolean ontabselected(int position, boolean wasselected) {                 viewpager.setcurrentitem(position, true);                 return true;             }         });     } 

viewpageradapter.java:

public class viewpageradapter extends fragmentpageradapter {     private final list<fragment> mfragmentlist = new arraylist<>();     private final list<string> mfragmenttitlelist = new arraylist<>();     private fragment currentitem;      public viewpageradapter(fragmentmanager manager) {         super(manager);     }      @override     public fragment getitem(int position) {         return mfragmentlist.get(position);     }      @override     public int getcount() {         return mfragmentlist.size();     }      public void addfragment(fragment fragment, string title) {         mfragmentlist.add(fragment);         mfragmenttitlelist.add(title);     }      @override     public charsequence getpagetitle(int position) {         return mfragmenttitlelist.get(position);     }      @override     public void setprimaryitem(viewgroup container, int position, object object) {         if (getcurrentitem() != object) {             currentitem = ((fragment) object);         }         super.setprimaryitem(container, position, object);     }      public fragment getcurrentitem() {         return currentitem;     } }